Customer match is one of the newer remarketing features from adwords, you upload a spreadsheet of your customers email addresses and can remarket to them in the traditional way.
The above video shows the process for this.
There are some policies for this and they can be found here
About the author
Thomas Green is a Certified Adwords Professional and specialises in direct response marketing. He has over 6 years PPC experience and has a straight forward approach to what works and what doesn’t!